One day Yao-shan Wei-yen (750-834), one of the well-known Chinese Ch'an master, was asked by the host of the monastery to give his sermon to the assembly who for a long while was expecting his teaching. Yao-shan said: "Strike the bell."
This is not so much a Zen question as a metaphysical one. So I will answer it in like kind. Eternity is comprised of every conceivalble variation. The begining, middle and end in each varient is already mapped out. So yes, everything is predetermined, and because you have the ability to chose by free will an altrrnate path, it is also true that you determin your fate,though your ideal destination may not be the outcome. It is like wandering a maze with infinite soloutions, each time you start again the linear story will appear diffrent.Yet all of it has already occured all at once within the blink of eternity.